The manufacture of disposable containers for various solid articles generally involves a highly developed technology and a multitude of cartons have been developed and used which incorporate closure latches which are integral with the carton. Specifically, various forms of cartons are in widespread use in which two closing sections are folded together, with the fold line serving as a hinge so that the carton can be repeatedly opened and closed. Integral latch structures have been included in such cartons in many different specific forms. One class of integral-carton latch structures employs a latch tab or flap extending from one part of the carton for mating engagement with a retainer on the other section and examples of such structures can be found in U.S. Pat. Nos. 3,537,251 (Edwards), 3,556,387 (Trimble) and 3,767,110 (Congleton). Generally, such integral-carton, latch structures require that the tab be inherently resilient and therefore rather severe limitations are imposed upon the material that may be employed in the carton. Additionally, the manner by which such members are stressed tends to determine the capacity of the closure. For example, a plain tab of carton material can offer only small resistance to bending forces but can effectively resist tension forces. As a result, the engagement between various members of conventional carton materials sometimes tends to be rather ineffective to resist forces that accidentally open the carton. Particular problems are found with the use of expanded plastic material, such as expanded polystyrene, as the carton material since tabs formed of such expanded material will tolerate only a limited repetition of flexure before breaking down. Accordingly, the manner by which the tabs are deformed to effect closure is rather important to the effective life and use of the carton. An additional problem which attends the use of expanded plastic material is that the highly effective insulating properties of such material can result in moisture condensation when a carton thereof is used to enclose a hot food item, such as a hamburger, or the like, with resultant sogginess of the food item. Some means of ventilation would therefore be desirable.
Accordingly, a need exists for an improved carton incorporating an effective integral latching mechanism. More specifically, important features of such a mechanism reside in the ability to maintain a carton closed, economy of manufacture, ability to withstand vibration and shock, ability to withstand repeated openings and closures, convenience of use and ventilating ability. Generally, the present invention provides an improved structure in view of such considerations.
Specifically, a carton is provided which comprises a pair of space-defining members with confronting closing edges which lock by means of a tab-latch. A portion of one of the walls forms a loop well adjacent its closing edge for receiving a tab carried in extension from an opposing closing edge. The tab is formed with a protuberance which deforms the loop during insertion therethrough and which is thereafter retained by the trailing edge of the loop. The outer rear edge surfaces of at least the terminal portion of the tab are in substantial contour conformance to the wall region rearwardly adjacent the loop for effecting close engagement. In a particular embodiment, the walls of at least the loop bearing member taper inwardly from its closing edge and the loop includes a trailing edge parallel to the wall so that the tab is directed inwardly against the wall region thereat forming an acute angle with the closing edge of the opposite member. The resulting configuration provides resistance to transverse forces which may otherwise tend to open the carton and additionally provides a close fitting relationship between the tab and the carton wall, decreasing the possibility of the tab portion being caught by misadventure during handling of the carton and thereby decreasing the incidence of tab breakage. The loop-protuberant tab configuration employed herein enables the carton to be repeatedly opened and closed with little wear and little change in the latching capability of the carton. Additionally, an integral hinge is provided and the closing edges are defined by flanges or lips which provide substantial overlap capability. Although not readily evident from a casual consideration of the foregoing, the present carton structure, containing such combination of elements and the loop-tab mechanism, provides a rearward shifting upon closure of the top member, revealing a passageway through the loop well which serves to ventilate the carton.